Types of Seams in Metal Working

Written by daisy cuinn

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A variety of seams are used to connect pieces of sheet metal in construction, auto body creation and fine art sculpture. The type of seam used depends largely on the application; some seams are created entirely by machine or in a metal shop, while others are made to snap together without requiring welding or soldering on site. In either case, metal seaming requires the proper equipment, knowledge and skills.

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Lap Seam

The lap seam is a basic metal seam where one piece overlaps the other. A "lap" is created by making a fold across the edge, then laying the lap over the other piece of metal, pounding flat and soldering, welding or securing with rivets. Lap seams are often used to connected two ends to make a cylinder and are used in making boilers, auto bodies, wall panels, metal sculpture and metal roofing.

Capped On Seam

Also known as the circular lap seam, the capped on seam is created by laying a flat round piece of metal over a smaller rounded piece such as the base of a cylinder. The overhang on the flat piece is folded over using a mallet. Once the fold is made, the seam is soldered. A capped on seam is used to make the bottom of a cylindrical metal drum or on the end of a round metal duct.

Folded Seam

A folded seam is made by folding the edges of both ends of the metal and hooking the folds together before pounding flat with a mallet and soldering. Folded seams are simple, but not as long-lasting or watertight as some newer, machine-made seams. Folded seams are traditionally used for industrial metal roofing, metal pipes and ductwork.

Grooved Seam

The grooved seam process is similar to the folded seam process; it involves connecting two folded edges, usually made with a machine, which are interlocked and pressure-tightened to make the seam. Manual grooved seams are pounded with a mallet to finish, with no soldering required. The lock seam, which has an additional fold and is often used for corner seams, is a type of grooved seam. The grooved seam is commonly used to construct objects made of light sheet metal such as air ducts.

Standing Seam

Widely used in roofing, the standing seam connects vertical metal roof panels with hidden fasteners. Standing seam roofs, also called snap-on or snap-lock because the seam fastens by pressing the ends together until it snaps, are popular because of their clean look and ability to prevent leaks better than the folded seam. Most metal roofing on residential homes are constructed with standing seams.

Cap Seam

In a cap seam, the ends are folded vertically at a 90 degree angle, butted together and held with a long metal cap that is secured with hidden fasteners. Cap seams are commonly used in commercial roofing and to create round, pointed roofs such as the top of a carousel. Cap seams on roofs are identifiable by the raised vertical "stripes" created by the caps and are sometimes chosen for aesthetics.